An Illinois firefighter who survived a heart transplant 10 years ago collapsed and died Saturday while fighting a fire at a mobile home park.

Dolton firefighter Lawrence Matthews Jr., 36, had stopped to catch his breath while helping to extinguish the large fire in the Chicago suburb of Harvey, WGN-TV in Chicago reported. He was leaning against a fence when he suddenly collapsed.

Matthews died of cardiac arrest about an hour later at Ingalls Memorial Hospital, the news station reported.

Matthews and his family celebrated the 10th anniversary of his heart transplant on June 2, just eight days before he died, NBC Chicago reported.

“I’m in shock. It’s a total loss,” Dolton Fire Chief Steven McCain told WGN-TV. “He was a family man. Four little ones. Loved his wife. Loved the job.”

Matthews defied the odds when he became a firefighter in 2009, two years after undergoing a heart transplant at the University of Chicago Medicine. A patient story on the hospital’s website said that Matthews overcame skeptics who didn’t believe he had the physical rigor to achieve his dream.

He did well on the department’s physical fitness tests, which included being able to run a timed mile, climb a 100-foot ladder and drag a 180-pound dummy out of a building.

Matthews also passed a required physical and was given the green light by his doctors to become a firefighter.

“The team often reminded me, before and after the transplant, about the need to live a normal life,” Matthews said in the profile. “It was up to me to how successful I would be.”

Matthews, who wanted to become a public servant from an early age, said he always possessed the drive to go after what he wanted.

“I believed I could become a firefighter,” he said. “The doctors gave me the confidence to do so. They told me to go for it, and that’s all I needed to hear.”

Matthews’ health problems began when he started experiencing shortness of breath at the age of 25, the hospital’s profile said. Doctors diagnosed him with cardiomyopathy, a disease that, according to the American Heart Association, can cause the heart to become enlarged, thick or rigid.

The structural changes to the heart make it weaker and less efficient at pumping blood through the body. Patients can suffer an irregular heartbeat or heart failure.

It was during his recovery that Matthews met his wife, Rachel, who worked in the cardiology clinic, the hospital said. The couple had a daughter and three sons, who range in age from 3 to 11 years old.

“It’s going to be tough,” McCain said of Matthews’ death. “It’s going to be something that the Dolton fire family, as well as the rest of the fire service family, is just going to have to deal with in the south suburbs.”

Dolton Mayor Riley Rogers said in a statement Monday that Matthews’ death leaves a “great emptiness” for the city.

“We did not simply lose a firefighter in the line of duty,” Rogers said. “Mr. Matthews was a man committed to saving the lives of others. A lifesaver has lost his life, and he will be deeply missed.”

It was not immediately clear if fighting the fire contributed to Matthews’ death, NBC Chicago reported.